Battery aging / degradation over time

Hi,

Here is the data you want. The chart is from THIS battery survey. If you enter your data, you can then go to charts page and select your username and it will show your entry in a different color on this chart. This way you can easily see if you are below or above the red trendline which shows the average.

We can clearly see a loss of capacity over time/use and definitely different numbers on vehicles with identical mileage. It's all expected. What is unexpected and encouraging is how the average shows that the loss degradation is slowing down and it seems to almost flatten out. In other words, everyone sees a loss of about 5% over the first 50k km and then only maybe 1% over the next 50k km.

Batteries definitely age both through time and use as well as temperature. All things factor in. Time alone seems to be a small factor. I remember a professor talking about Lithium batteries and he said keeping a Lithium battery at a low temperature and state of charge and it will be preserved for many years. The warmer it gets the faster they age. The more you cycle, the faster they age and so all adds up.

David99 said:

We can clearly see a loss of capacity over time/use and definitely different numbers on vehicles with identical mileage. It's all expected. What is unexpected and encouraging is how the average shows that the loss degradation is slowing down and it seems to almost flatten out. In other words, everyone sees a loss of about 5% over the first 50k km and then only maybe 1% over the next 50k km.

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I thought that was expected too, at least from some article i read. 3-5% for the first 50k miles. Then 1-2% every 30k miles

Max* said:

I thought that was expected too, at least from some article i read. 3-5% for the first 50k miles. Then 1-2% every 30k miles

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Well, I have three years and more km than your chart shows. I have 7% loss. I charge at 30 amps, rarely supercharge, never to full. I think that it is mainly heat and time, not miles. This chart does not tell us what causes degradation. But it nicely shows degradation tapers off after a few years.

Interestingly, Tesla has been keeping data from the first. They don't share much, but THEY say it's time, not mileage. You notice their drive train warranty states "Eight years, UNLIMITED miles".

But what do they know, right?

I have lost 2.2% in one year and 14K mi. I have lost 5mi at the daily charge level. It seems like I have lost the range in just the last two months. It has been unusually warm in Coastal CA this year and I wonder if that has anything to do with it. I have really noticed it in the last two weeks, when we were in the 90-105 temp range. I charge to the daily mark almost every night at 40 AMPs. I have only charged to 100% twice and have used superchargers a handful of times. I wonder if I should charge to a lower level, per the previous comments. Even though it is only 5mi, I almost did not make it home one night, due to rude people not moving their cars from chargers when they were finished, with less than 1mi to spare, so it really can matter.

I've lost 1 mile of rated range over the course of 18 months and 22,000 miles, and I live on Maui where it is always above 80 degrees. In fact, we've had a very warm year, with more 90 degree days than I can remember in my many years of living here. I NEVER charge to less than 90%, except on very rare occasions. I now charge at 240V/40 amps, but most of my first 6 months were 115V/12 amps.

I've lost 4 rated miles in 11 months/37,000 miles. They seem to have disappeared suddenly after two separate firmware updates. I'm tempted to ascribe them to changes in the calibration of the rated miles calculation.

wga22 said:

thank you for the quick replies. I see the chart is done by distance, and wonder if its really age that is more of a factor. Either way, I agree, the battery ages similar to what we see in our cell phones that there is a quick fall off, then plateaus, as the chemistry of the batteries stabilize.

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Degradation comes from both use (charge-discharge cycles) and from ageing. These effects are not additive. Rather, in most cases use should be the main driver of degradation. Time spent at very high or low state of charge, depth of discharge cycles, temperature and overall useage are the most important factors here. If a battery is in little use however, pure ageing will be the main driver of degradation.

roblab said:

Well, I have three years and more km than your chart shows. I have 7% loss. I charge at 30 amps, rarely supercharge, never to full. I think that it is mainly heat and time, not miles. This chart does not tell us what causes degradation. But it nicely shows degradation tapers off after a few years.

Interestingly, Tesla has been keeping data from the first. They don't share much, but THEY say it's time, not mileage. You notice their drive train warranty states "Eight years, UNLIMITED miles".

But what do they know, right?

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Not my chart.

I found the link, it's 6% for the first 50k miles, then 1% for every 30k miles, my memory was close: Tesla Model S Battery Life: How Much Range Loss For Electric Car Over Time?

You posted your car for sale with 80k miles. 6% + 1% = 7%, so seems that you're in line with expectations.

evp said:

I've lost 4 rated miles in 11 months/37,000 miles. They seem to have disappeared suddenly after two separate firmware updates. I'm tempted to ascribe them to changes in the calibration of the rated miles calculation.

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Me 2

I have 45k miles now on a 2 yr old P85+. Rarely supercharged and rarely go beyond 90% unless for several road trips. Charging rate of 28amps and staying around the 75% mark. Recently had a road trip to Southern California and at 100%, I am at 252 miles now.

Johan said:

Degradation comes from both use (charge-discharge cycles) and from ageing. These effects are not additive. Rather, in most cases use should be the main driver of degradation. Time spent at very high or low state of charge, depth of discharge cycles, temperature and overall useage are the most important factors here. If a battery is in little use however, pure ageing will be the main driver of degradation.

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A slightly different question about degradation: let's say you drive just 10 or 20 miles a day and recharge each night. Is a long history of shallow discharge cycles like that bad for the battery's health? Or should you more deeply discharge cycle the battery periodically?

I assume from the statement above that the answer is "no" ?

f-stop said:

A slightly different question about degradation: let's say you drive just 10 or 20 miles a day and recharge each night. Is a long history of shallow discharge cycles like that bad for the battery's health? Or should you more deeply discharge cycle the battery periodically?

I assume from the statement above that the answer is "no" ?

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Shallow cycles are better. Also staying away from the highest and lowest states of charges (=voltages), especially the high voltages is better. In your example that would mean charging to say 50% and driving 20 miles down to 40-something % every day.

The only benefit of an occasional full(ish) cycle is better balancing of the battery pack and a better calibration of the range estimation.

No matter how little you cycle the battery and no matter how well you are able to stay away from high or very low voltages there's no away around pure ageing though.

thanks Johan - this is good info to know

I don't believe the theory time being the main factor over use. I have 60k miles yet cars with the same mileage that are much older than mine have the same degradation. So if time was the more important factor it would certainly show more impact.

The curve is definitely steeper at first and eventually levels out. Could explain why at 60 K you show essentially the same numbers as someone at 80 K.

David99 said:

I don't believe the theory time being the main factor over use. I have 60k miles yet cars with the same mileage that are much older than mine have the same degradation. So if time was the more important factor it would certainly show more impact.

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For the vast majority of use cases the time factor will be irrelevant. Any effect of ageing will simply be overpowered by degradation from use for almost all cars. If you were a car collector though, with the car just sitting in a garage plugged in and kept at 30% SOC or something the battery would still degrade though over time, that's all I'm saying.